Britain – Largest, last and costliest RAID ON LONDON by bomber aircraft: 28 of 38 Gothas sent (6 lost, 1 crashes), 3 Giants with 600 (14.3t) bombs in 1 hour cause 226 casualties (night May 19-20). Anti-aircraft fire destroys 2 Gothas, 88 defence sorties shoot down 3 Gothas in 11 interceptions.
France: Heavy German raids on railways and munition dumps (12,500t ammo destroyed until May 22) by Bogohl 6 (and on May 20-21); 935 further British soldiers wounded and nurses killed or injured in 15-plane Gotha raid (1 shot down) on Etaples hospital complex (key rail bridge missed) at night May 19-20, repeated (night May 30-31, 47 casualties) when one span of bridge hit, but alternative soon in use (short traffic breaks on June 30 and July 24).
France: Fayolle diary ‘… still discord between Petain and Foch. They … ought to be … one single man’.
Flanders: British raid southwest of Meteren, and northwest of Merville (May 20). French attack near Locre (Kemmel) bags 400 PoWs on May 20.
Irish Sea: US destroyers Patterson and Allen depth charge and sink new coastal submarine UB-119 west of Cardigan Bay.